Method for producing a coating of flourescent material

ABSTRACT

A method for producing a coating of fluorescent or luminophore material includes the steps of depositing the luminophore material from a vapor phase on a substrate in such a manner that at least 30 weight-% of the luminophore material used is deposited on the substrate and then abrading or polishing the luminophore coating to a predetermined even layer thickness utilizing a polishing agent.

[0001] The invention is directed to a method for producing a luminophore layer.

[0002] DE 195 16 discloses a method for producing a luminiferous layer composed of CsI:Tl. It is thereby provided that the pressure in the vapor-deposition system is higher than the vapor pressure of the thallium iodide, at least during the vapor-deposition. A luminophore layer whose light yield is improved can be produced based on this method.

[0003] DE 198 52 326 A1 discloses a method that is particularly suited for coating a substrate with GaBr-doped luminophores. The luminophore is thereby placed onto a heated evaporation source in a vacuum in the vapor-deposition chamber, said luminophore immediately vaporizing thereat and depositing on the substrate.

[0004] DE 44 29 013 A1 discloses an apparatus for the vapor-deposition of a substrate having an X-ray measuring instrument for measuring the layer thickness. The vapor-deposition rate is regulated dependent on the measured result of the layer thickness measurement in order to achieve an optimally uniform layer thickness.

[0005] DE 24 35 629 A1 discloses a method for smoothing the surface of a luminophore layer applied on a substrate. The surface is thereby worked with forging bodies in the fashion of forging.

[0006] DE 28 32 141 A1 discloses a method for manufacturing radiation converter screens, whereby a luminophore layer applied on a substrate is ground and polished for achieving a uniform layer thickness. Irregularities that project above the luminophore layer are thereby in fact eliminated. However, relatively long-wave irregularities are generated when grinding and polishing. Moreover, relatively large grinding agent grains are worked into the luminophore layer during grinding. These reduce the optical quality of the luminophore layer.

[0007] In order to counter this disadvantage, attempts have already been made in the Prior Art to arrange the luminophore source at as great a distance as possible from the substrate in the vapor-deposition. Luminophore layers deposited in this way are relatively uniform in terms of their layer thickness. However, a great deal of material must be utilized here in the vapor-deposition because only about 10 weight-% of the evaporated material are deposited on the substrate here.

[0008] An object of the invention is to eliminate the disadvantages of the Prior Art. In particular, a method should be specified with which a luminophore layer having an optimally uniform layer thickness can be manufactured in an optimally simple way.

[0009] This object is achieved by the features of claim 1. Expedient developments derive from the features of claims 2 through 10.

[0010] In conformity with the invention, a method for producing a luminophore layer comprising the following steps is provided:

[0011] a) deposition of the luminophore from the vapor phase on a substrate such that the spacing of the luminophore source from the substrate is selected such that at least 30 weight-% of the utilized luminophore are deposited on the substrate; and

[0012] b) abrasive erosion of the luminophore layer to a prescribed, uniform layer thickness by means of a polishing agent.

[0013] The economic feasibility of the method is enhanced in that at least 30 weight-% of the utilized luminophore are deposited on the substrate. A uniform layer thickness can then be achieved by means of a following, abrasive erosion of the luminophore layer with a polishing agent.

[0014] Expediently, the substrate is rotated during step a). A sponge or felt manufactured of plastic is advantageously employed as polishing agent. Powdered luminophore can be contained in the sponge or felt. Expediently, this is thereby a matter of the same luminophore that has been deposited on the substrate. Doped alkali halides such as, for example, CsI:Na, CsI,Tl or CsBr:Eu thereby particularly come into consideration as luminophore. What the inclusion of the powdered luminophore in the sponge or felt during the abrasive erosion achieves is that fissures in the luminophore layer are filled out with the powdered luminophore.

[0015] The abrasive erosion can be implemented by means of a non-aqueous liquid, preferably, ethanol, silicone oil or cyclohexane.

[0016] Corundum or diamond particles can be added to the liquid. The rate of the erosive abrasion can thus be increased.

[0017] According to another design feature, the layer thickness distribution of the deposited luminophore layer can be measured topically resolved before step b), and the corresponding data can be stored. For the implementation of such a topically resolved measurement, the luminophore layer deposited on the surface of the substrate can be measured with a probe of a CNC measuring machine or with an optical method such as, for example, oblique light laser interferometry. Measuring the layer thickness by means of X-ray absorption measurement also comes into consideration. A pressing power whose size is inversely proportional to the measured layer thickness can be applied onto the polishing agent. I.e., the pressing power on the polishing agent is increased where the layer thickness is high. Further, the relative speed of the substrate relative to the polishing agent can be inversely proportional to the measured layer thickness. I.e., the rotational or, respectively, circumferential speed of the substrate is especially high at locations where the measured layer thickness is low; it is low where the measured layer thickness is high. The above-described method for abrasive erosion is expediently implemented computer-assisted and upon employment of the measured data. The polishing agent, for example, can thereby be radially moved over the rotating substrate.

[0018] An exemplary embodiment of the inventive method is explained in greater detail below on the basis of the drawing. Shown are:

[0019]FIG. 1 a picture of an inhomogeneity in a luminophore layer made with a scanning electron microscope;

[0020]FIG. 2 a picture of a fracture edge of a luminophore layer through an inhomogeneity made with a scanning electron microscope; and

[0021]FIG. 3 a picture onto the surface of a luminophore layer made with a scanning electron microscope.

[0022] For producing a luminophore layer for a radiation converter screen, a substrate manufactured, for example, of a planar aluminum disk is introduced into a known vapor-deposition system. Such a vapor-deposition system is known, for example, from DE 195 16 450 C1, whose disclosure is herewith incorporated. The temperature of the substrate is set such that the saturation vapor pressure over the luminophore layer condensing on the substrate is lower than the vacuum prevailing in the vapor-deposition. A luminophore layer having a thickness of approximately 500 μm is vapor-deposited. The spacing between the source of the luminophore to be evaporated and the substrate is thereby selected such that at least 30 weight-%, preferably 50 weight-%, of the evaporated luminophore precipitate on the substrate.

[0023] In particular, the vapor-deposited luminophore layer comprises the punctiform inhomogeneities shown in FIGS. 1 and 2, these being caused by giant grain growth. In addition, a non-uniform layer thickness distribution on the substrate caused by the vapor-deposition can occur.

[0024] For producing a uniform layer thickness, the luminophore layer is reduced to a prescribed, uniform layer thickness by means of a polishing agent. A felt, preferably a plastic felt, or a polishing agent equipped with plastic bristles is expediently employed as polishing agent. The polishing ensues wet, preferably with a non-aqueous liquid, for example ethanol, silicone oil or cyclohexane. Diamond particles can be added to the liquid. Luminophore particles can be contained in the polishing agent in order to fill fissures that may potentially be present at the surface of the luminophore layer. To that end, the polishing agent is expediently placed into a saturated aqueous solution of the luminophore to be polished and is subsequently dried.

[0025] The measurement of the layer thickness of the luminophore layer applied onto the substrate ensues, for example, with the probe of a CNC measuring machine, an optical method such as, for example, oblique light laser interferometry or by means of X-ray absorption measurements.

[0026] The data acquired in the layer thickness measurement are made available to a polishing device that works according to the zonal correction principle. Such a polishing device is available, for example, from JenOptik AG under the name “Feinkorrekturmaschine FK 300”. With such a polishing device, a low circumferential speed of the substrate and—at the same time—a high pressing power onto the substrate is [sic] set at locations of high layer thickness. A higher circumferential speed and a lower pressing power is [sic] set given a low layer thickness. The control of the circumferential speed, of the pressing power and the radial position of the grinding [sic] agent relative to the rotating substrate ensues automatically, preferably computer-assisted.

[0027] The inventive method succeeds in setting the layer thickness of the luminophore layer with a deviation of less than 2%. In the case of a luminophore layer produced, for example, of CsBr:Eu, this corresponds to a maximum layer thickness deviation of less than 10 μm.

[0028] Another advantage of the inventive method is comprised therein that fissures located at the surface of the luminophore layer, as shown, for example, in FIG. 3, are simultaneously closed by the luminophore particles contained in the polishing agent. 

1. Method for producing a luminophore layer, comprising the following steps: a) depositing the luminophore from the vapor phase on a substrate such that at least 30 weight-% of the utilized luminophore are deposited on the substrate; and b) abrasive erosion of the luminophore layer to a prescribed, uniform layer thickness by means of a polishing agent.
 2. Method according to claim 1, whereby the substrate rotates in step a).
 3. Method according to one of the claims 1 or 2, whereby a sponge or felt manufactured of plastic is employed as the polishing agent.
 4. Method according to one of the preceding claims, whereby powdered luminophore is contained in the sponge or felt.
 5. Method according to one of the preceding claims, whereby the abrasive erosion is implemented by means of a non-aqueous liquid, preferably ethanol, silicone oil or cyclohexane.
 6. Method according to one of the preceding claims, whereby corundum or diamond particles are added to the liquid.
 7. Method according to one of the preceding claims, whereby the distribution of layer thickness of the deposited luminophore layer is measured topically resolved before step b), and the corresponding data are stored.
 8. Method according to one of the preceding claims, whereby a pressing power whose size is inversely proportional to the measured layer thickness is applied onto the polishing agent.
 9. Method according to one of the preceding claims, whereby the relative speed of the substrate relative to the polishing agent is inversely proportional to the measured layer thickness.
 10. Method according to one of the preceding claims, whereby the abrasive erosion is implemented computer-assisted upon employment of the measured data. 